The present invention relates to a method and apparatus for controlling an electric drive motor of a motor vehicle windscreen wiping system in at least two different speed steps by a manually-operated multi-step windscreen wiper control switch, in which the drive motor can be automatically switched from at least one speed step switched on by the control switch into a lower speed step independently of the control switch, when the travelling speed of the vehicle passes through a predetermined threshold value from a higher speed.
A method can be derived from the operation of a known switching arrangement (German Patent Document DE 30 21 877 A1) for the intermittent operation of a windscreen wiper motor of motor vehicles. In this known circuit arrangement, the operation or the wiping interval period of the wiper motor in one of three operating positions of the windscreen wiper control switch depends on a threshold value of the travelling speed. Above the threshold value, the wiping interval pause becomes zero, that is to say the windscreen wiper motor operates in continuous mode. Below the threshold value, the wiping interval pause assumes a particular value which is different from zero and which can be fixed or manually/automatically variable.
Due to this purely speed- or also rotational speed-dependent automatic switching to a next lower wiping speed, however, the requirements of the vehicle user for clear vision even when his vehicle is travelling more slowly or standing still is not always adequately met under disadvantageous circumstances, for example with a rapidly changing density of precipitation.
Although the vehicle user can manually set a different position of the control switch at any time, the automatic switching to a slower wiper speed is then no longer available with the known circuit arrangement.
If the automatic wiping speed switching of the known circuit arrangement were to be applied to all speed steps of the windscreen wiper drive motor, it would no longer be possible at all, for example, to switch to the fastest wiper step below the travelling speed threshold value.
It is also known (from German Patent Document DT 25 03 767 C2) to switch a drive motor of a windscreen wiping system of a motor vehicle from continuous to intermittent operation, that is to say to the next lower speed step in dependence on a threshold value of its current consumption. With a high current consumption, the system concludes that there is little wetting of the area to be wiped, that is to say a small quantity of impinging rain, so that the system can then automatically switch to intermittent operation for relieving the vehicle user. By the same token, the vehicle user can also arbitrarily activate the windscreen wiper or wipers within such an automatically switched-on wiping interval by means of a separate (foot) switch while shortening the interval.
It is known (German Patent Documents DT-OS 1 530 979, DE 35 27 406 A1) to vary the duration of wiping intervals of a windscreen wiping system continuously in dependence on the travelling speed of a vehicle, in which arrangement short wiping intervals up to continuous operation are generated with a relatively high travelling speed and longer wiping intervals are generated with a relatively low travelling speed. Although it is not necessary to provide a control switch having several switch positions in these arrangements, the vehicle driver also does not have any direct influence on the operation of the windscreen wiping system.
A control device for the continuous and/or intermittent operation, particularly of windscreen wipers, is known (DT 24 03 311 A1) which makes it possible, on the one hand, to read in and to store wiping intervals of a windscreen wiper by successively operating the windscreen wiper control switch. In this known device, the windscreen wiper can be switched from intermittent (interval) mode to continuous mode by this means, in that the control switch is briefly switched to a second wiper step or, the control switch is switched off and on again twice in succession for a short time or, the control switch is switched off and on again once during the wiper run.
In this non-generic control device, in contrast, an automatic switching which is dependent on the travelling speed from one wiper speed step to the next lower, is not provided.
Because continuous operation of the wiper should be automatically guaranteed when the control unit is switched on by the vehicle user, there is also no predetermined interval period stored for the intermittent operation. Instead, it must be read in and stored again each time, as required, by appropriately operating the control switch.
An object of the present invention is to provide a method in which the driver can override the automatic operation of the control circuit in a simple manner and provide a device that can carry out this method.
This and other objects are achieved by the present invention which provides a method for controlling an electric drive motor of a motor vehicle windscreen wiping system in at least two different speed steps by a manually-operated multi-step windscreen wiper control switch, the drive motor being automatically switchable from at least one speed step switched on by the control switch when a travelling speed of the motor vehicle passes through a predetermined threshold value from a higher travelling speed into a lower speed step independently of an operation of the control switch, and comprises overriding the automatic switching by switching on a speed step that is selected by manual operation of the control switch from the automatically switched-on lower speed step.
The objects are also achieved by the present invention which provides a device for controlling a motor vehicle windscreen wiping system in multiple speed steps. The device comprises a windscreen wiper control switch which is manually switchable into multiple operating positions, and means for controlling a drive motor into speed steps selectable by the operating positions of the control switch. A threshold value switch is supplied with an electrical signal that is proportional to the travelling speed of the motor vehicle, and has an output coupled to an input of the means for controlling, this threshold switch providing a threshold value switching signal which, when it passes through a predetermined threshold value in a particular direction, causes the means for controlling to automatically switch the drive motor from a currently switched-on speed step into a lower speed step. The means for controlling includes a switching device, coupled to the control switch and activatable by manual operation of the control switch when the travelling speed of the vehicle is below the threshold value of the travelling speed. The switching device cancels a current automatic switching of the speed step of the drive motor to the next lower speed step and the control switch is manually operated below the threshold value, and switches on the speed step of the drive motor selected by the manual operation of the control switch.
When the method according to the present invention is applied or when using the device according to the present invention, the vehicle user can override the intervention of the automatic switching system as desired by an arbitrary actuation of the control switch for the windscreen wiper drive motor. Thus, the driver can either switch to a different wiper speed step, which is then not affected by the automatic switching system which is expanded to all speed steps, or can manually reactivate the speed step which was deactivated due to the automatic switching after the speed had dropped below the predetermined travelling speed value. Any such manual intervention has priority until the speed again drops below the threshold value of the travelling speed from above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.